With the recent downsizing of communication devices and electronic devices, piezoelectric oscillation devices, such as crystal resonators for angular velocity sensors, are also required to be smaller. Tuning-fork type crystal vibrators comprising a pair of vibrating arms are used for crystal oscillation devices for high precision clocks and gyroscopes. The crystal tuning forks used for those crystal oscillation devices are produced from quartz wafers by a process including photo resist coating, photolithography and wet-etching. Several hundred to several thousand contours of crystal tuning forks are formed on a quartz wafer. Subsequently, an electrode pattern is formed on each of the several hundred to several thousand of crystal tuning forks by a process including photo resist coating, photolithography and wet-etching, using a method such as that disclosed in Japanese Unexamined Patent Publication No. 2005-134364.
FIG. 10 depicts an enlarged view of the basal portion 29 of a crystal tuning fork 20. FIG. 10a illustrates a cross-sectional view of a pair of vibrating arms 21 and the basal portion 29 across the YZ plane, while FIG. 10b illustrates a cross-sectional view of a pair of vibrating arms 21 and the basal portion 29 across the XY plane. In recent years, the width of each vibrating arm of the crystal tuning fork 20 is typically about 0.1 to 0.2 mm, and the gap between the arms 21 is also typically about 0.1 to 0.2 mm.
Quartz wafers are cut out from Y-bar or Z-plate synthetic quartz crystals with predetermined crystal orientations. The etching rate of a quartz wafer, from which the crystal tuning forks 20 are etched out, depends on the crystal orientation, the wafer having a direction in which the etch rate is higher, or lower, than other directions. As a result, bumps and grooves as shown in FIGS. 10(a) and (b) are formed in the area between the roots (hereinafter denoted as “root area”) 261 of the pair of vibrating arms 21, when the quartz wafer is wet-etched from both the surfaces. With such bumps and grooves, the photoresist, coated to form an electrode pattern on the crystal tuning fork 20, tends to accumulate in the root area 261 of the vibrating arms 21. The bumps may also cause insufficient exposure at the time of the photolithography (exposure) of the electrode pattern. As a result, there has been a problem that many electrodes are short-circuited in the root area 261 of the pair of vibrating arms 21 when forming electrode patterns on crystal tuning forks. This hinders productivity and quality of the crystal tuning forks.